1. Field of the Invention
The present invention relates to an electromagnetic relay and a contact spring assembly for the electromagnetic relay, and more particularly, to an electromagnetic relay used in a telephone exchange or the like and a contact spring assembly for the electromagnetic relay.
2. Description of the Related Art
Traditionally, lightning surge protection has been required for subscriber circuits in telephone exchanges. Since implementing this lightning surge protection capability with semiconductor devices is extremely costly, a plurality of electromagnetic relays are used in every subscriber circuit accommodated in a telephone exchange.
In recent years, reductions in size and power consumption have been demanded in various kinds of apparatus. For telephone exchanges also, the need has been increasing to reduce the size, cost, and power consumption of the telephone exchange by reducing the number of electromagnetic relays used.
Namely, in the telephone exchange, for example, three electromagnetic relays are provided for each subscriber circuit in the exchange, of which two electromagnetic relays control a connection operation of a test circuit to switch the mode between normal operation mode and test mode. The remaining electromagnetic relay is used for dial pulse transmission. Note that, in the test mode, all the connections on the three electromagnetic relays are reversed from that of the normal operation mode and testing is performed by the test circuit. The testing by the test circuit is, for example, performed once a day or once every few days, to check the impedance, connection, etc. from the exchange to the subscriber.
As described above, for each subscriber circuit (test circuit) in the telephone exchange, for example, three electromagnetic relays (two for the test circuit), each with two transfer contact spring sets, have been used. Since these electromagnetic relays have to be provided for each subscriber circuit, such a configuration has been a major factor working against a reduction in the size and cost of the exchange.
The prior art electromagnetic relays and contact spring assemblies for the electromagnetic relays and problems thereof will be described in detail later with reference to the drawings.